1. Field of the Invention
The present invention generally relates to packages for containing electronic devices. More particularly, this invention relates to a ceramic package requiring a deep cavity for enclosing an electronic device, such as an infrared sensor, wherein the package is configured to be more readily fabricated.
2. Description of the Related Art
Hermetically-sealed ceramic packages are used to enclose a variety of semiconductor sensing devices, such as infrared (thermal) sensors, yaw (angular rate) sensors, angular and linear accelerometers, pressure sensors, etc. Each of these devices typically involves one or more micromachined sensing structures or elements formed in or on a silicon chip (referred to herein as a device chip). The device chip is often placed within a protective package and then wire bonded to electrically connect the device to bond pads on the package. An example of this packaging scheme is represented in FIG. 1, which shows a device chip 10 placed within a deep cavity 14 defined entirely by a recess 16 in a ceramic base 12, and then closed by a ceramic lid 18. The device chip 10 is represented as having a diaphragm on which an infrared sensing element 20 is fabricated, such as of a type disclosed in commonly-assigned U.S. Patent Application Publication No. 2003/0146384 to Logsdon et al., U.S. Pat. No. 6,793,389 to Chavan et al., or U.S. Patent Application Publication No. 2003/0148620 to Chavan et al., though the device chip 10 could be fabricated to carry a variety of other types of sensing elements.
The sensitivity of the infrared sensing element 20 is enhanced if the cavity 14 is evacuated, necessitating that the lid 18 is hermetically sealed with the base 12. An optical lens or window 22 is provided in the lid 18 through which infrared radiation to be sensed can be transmitted into the cavity 14 and to the sensing element 20. A consideration in the fabrication of the package shown in FIG. 1 is to provide sufficient focal distance for incoming infrared radiation after passing through the window 22 in the lid 18 and before impinging the sensing element 20. However, optimizing the focal length requires a relatively deep recess 16 in the base 12, which complicates the fabrication of the base 12 and incurs additional costs.
From the above, it can be appreciated that packages required for sensing elements can add significant cost to a sensor, and that it would be desirable if the cost and complexity of such packages could be reduced, particularly for the case of infrared sensors.